The present invention relates to a projection image display apparatus for enlarging/projecting an image outputted from an image generating source, for example, a projection TV by a projection lens onto a screen, and a projection optical system employed in this projection image display apparatus. More specifically, the present invention is directed to such a projection image display apparatus suitable for increasing a color purity, and further for improving focus performance and contrast without deteriorating brightness of an image.
While various image sources are required, rear projection image display apparatus have be widely marketed as large screen projection optical apparatus in view of light weight, low cost, and compact needs.
Within a cabinet of this rear projection image display apparatus, there are provided three projection tubes and projection lenses corresponding to the respective projection tubes. These three projection tubes independently produces red, green, blue-colored image light, respectively, as an image generating source (will be referred to as xe2x80x9cred, green, blue image light projection tubesxe2x80x9d hereinafter). Then, original images displayed on fluorescent planes, or fluorescent faces of the respective red, green, blue image light projection tubes are enlarged/projected onto a screen by the projection lenses so as to be synthesized with each other, so that a full color image may be displayed.
This rear projection image display apparatus is disclosed in, for instance, JP-A-3-224384, and employs the colored lens element in order to give the wavelength selecting characteristic (filtering effect) to the projection lens used in the green image light projection tube. This display apparatus uses the colored lens element so as to reduce a spurious component close to the red and blue wavelengths involved in the light emission spectrum of the fluorescent substance of the green fluorescent plane. As a result, the color reproduction range of the enlarged image displayed on the screen is expanded, the color aberration is reduced, and the focus performance is improved. Furthermore, the concave lens element located near the fluorescent plane of the projection tube is colored, so that the unnecessary light component which is reflected on the light projection (emission) plane thereof and then is returned to the fluorescent plane can be absorbed/reduced two times. Accordingly, the contrast performance can also be improved.
In addition, very recently, as described above, in order that the projection lens employed in the red image light projection tube other than the projection lens employed in the green image light projection tube is equipped with the wavelength selecting characteristic (filtering effect), the colored lens element is employed in the rear projection image display apparatus. This colored lens element causes the spurious component close to the green wavelength involved in the light emission spectrum of the fluorescent substance of the red fluorescent plane, to be reduced, so that the color reproduction range of the enlarged image displayed on the screen can be expanded. Similar to the green image light projection tube, since the concave lens element located close to the fluorescent plane of this red image light projection tube is colored, the contrast performance can also be improved at the same time.
On the other hand, brightness of the normal display apparatus is represented by luminance of a white color projected on a screen in an enlargement manner. When a white color is displayed by an actual display apparatus, in the case that chromaticity of each of red, green, blue image light is constant, the red image light is mixed with the blue image light in a preselected luminance ratio, while using the green image light as the reference, which may highly control the brightness. To produce necessary luminance on the fluorescent plane of each of the projection tubes, each of the cathod currents must be set to a predetermined current value based upon the cathod current-to-luminance characteristics of the respective projection tubes.
In this case, as previously explained, when the colored lens elements are employed in order that the wavelength selecting characteristics (filtering effects) are given to the projection lens used in the green image light projection tube and also the projection lens used in the red image light projection tube, the resultant color purity is increased. However, since a portion of the light component which constitutes the major portions of the green image light and the red image light is also absorbed by the colored lens elements to be thereby attenuated, there is such a problem that the brightness is lowered.
Also, the transmission projection type screen is constructed by combining a plurality of transparent resin. As a result, when the ambient light such as illuminating light is entered into the screen, a portion of this entered ambient light is reflected on the surfaces of the internal transparent resin, and then is returned to the light incident side. Since this returned ambient light is superimposed with the image light which has passed through the screen, this may cause the contrast performance of the displayed image to be lowered.
Conventionally, a lenticular sheet is employed as one of the transparent resin used in this transmission projection type screen, a light absorption layer is provided between the respective longitudinal lenticular lenses provided on the light projection plane thereof, and then the ambient light is absorbed by this light absorption layer. As a consequence, the light amount of the ambient light entered into this lenticular sheet is reduced. However, since the ambient light is entered from the portion of the longitudinal lenticular lens of this lenticular sheet, the resultant contrast performance is lowered by the ambient light which is reflected inside the screen and then is returned.
The present invention has been made to solve the above-described problems, and has an object to provide a projection image display apparatus capable of suppressing lowering of brightness of a displayed image to thereby improve focus performance and contrast performance, and capable of increasing a quality of the displayed image.
Another object of the present invention is to provide a projection image display apparatus capable of suppressing a reduction in brightness of a displayed image to thereby reducing an adverse influence caused by reflections of ambient light.
To achieve the above-explained objects, a projection image display apparatus, according to an aspect of the present invention, is featured by that a light transmitting means having a preselected light transmittance characteristic is provided with a lens element of a projection lens corresponding to a green image light projection tube and also a lens element of a projection lens employed in a red image light projection tube so as to reduce unwanted spurious components in the image light generated from the green image light projection tube and the red image light projection tube, and further to increase transmittance of a major component. In particular, when this light transmitting means is provided with a concave lens element located close to a fluorescent plane of the projection tube, the unwanted light components which are reflected on the light projection plane thereof and then is returned to this fluorescent plane are absorbed and reduced two times. As a consequence, contrast performance can be improved.
Also, to achieve another object, a screen, according to another aspect of the present invention, is featured by that a light transmitting means is provided with a transmission projection type screen, and this light transmitting means attenuates energy to a value smaller than, or equal to a predetermined value in a wavelength region other than wavelengths xcex Rmax, xcex Bmax, xcex Gmax of peak energy of a spectral distribution in each of image light produced from each of red, green, blue image light projection tubes.